The present application relates to a hologram recording film and a method of manufacturing same, and an image display apparatus.
Virtual image display devices (image display devices) using a hologram diffraction grating so as to allow an observer to observe a two-dimensional image generated through an image forming device as an enlarged virtual image through a virtual image optical system have been made public through, for example, Japanese Unexamined Patent Application Publication No. 2007-11057.
The above-described image display device, that is, an image display device 100 includes, for example, an image forming device 111 configured to form and display an image, a collimating optical system 112, and a virtual image optical system (optical device 120) onto which a light beam emitted from the image forming device 111 is made incident and by which the light beam is led to eyes 60 of the observer. Here, the optical device 120 includes a light guide plate 121, and first and second diffraction grating members 130 and 140 that are provided on the light guide plate 121. A light beam emitted from each of pixels of the image forming device 111 is made incident on the collimating optical system 112, and the collimating optical system 112 generates a plurality of collimated light beams that are made incident on the light guide plate 121 at angles different from each other, and the collimated light beams are made incident on the light guide plate 121. The collimated lights are made incident and emitted from one optical face (first face) 122 of the light guide plate 121. Further, the first and second diffraction grating members 130 and 140 are secured to the other optical face (second face) 123 of the light guide plate 121, the optical face 123 being parallel with the first face 122.
The collimated light beams that are made incident on the light guide plate 121 at the different angles from the first face 122 are made incident on the first diffraction grating member 130, and each of the collimated light beams is diffracted and reflected, as it is. Then, the diffracted and reflected collimated light beam travels while being totally reflected repetitively between the first and second faces 122 and 123, and is made incident on the second diffraction grating member 140. The collimated light beam which is made incident on the second diffraction grating member 140 does not satisfy the total reflection condition by being diffracted and reflected, and is emitted from the light guide plate 121 and led to the eyes 60 of the observer.
Each of the first and second diffraction grating members 130 and 140 includes a reflection-type volume hologram diffraction grating in which interference fringes are formed. Each of the first and second diffraction grating members 130 and 140 should be provided with a wide diffraction wavelength band. Namely, three primary-color light beams including a red light beam, a green light beam, and a blue light beam that are emitted from the image forming device 111 should be diffracted and reflected. Consequently, the interference fringes formed in the reflection-type volume hologram diffraction grating are duplexed. Otherwise, multiple diffraction grating layers are provided.
Here, a Bragg condition for attaining diffraction and reflection in the diffraction grating member is expressed through Equation (A) that follows. In Equation (A), the sign m denotes a positive integer, the sign λ denotes a wavelength, the sign d denotes a pitch defined on a grating surface (which denotes an interval defined in the direction of the normal of a virtual plane including the interference fringes, and is hereinafter referred to as a “grating surface pitch”), and the sign Θ denotes the complementary angle of an angle at which a light beam is made incident on the interference fringe. The slant angle (inclination angle) φ of the interference fringes denotes an angle which the surface of the diffraction grating member forms with the interference fringe. The interference fringes are formed so as to extend from the inside the diffraction grating member to the surface of the diffraction grating member, as is the case with the following descriptions. Further, the relationships between the complementary angle Θ, the slant angle φ, and an incident angle ψ that are obtained when a light beam enters the diffraction grating member at the incident angle ψ are as shown in Equation (B), and illustrated in FIG. 10B. Further, the pitch Λ of the interference fringes observed on the surface of the diffraction grating member is as shown in Equation (C). Hereinafter, the above-described pitch Λ will be referred to as a “surface pitch” so as to be distinguished from the grating surface pitch d. The surface pitch Λ is illustrated in FIG. 10B.m·λ=2·d·sin(Θ)  Equation (A)Θ=90°−(φ+ψ)  Equation (B)Λ=d/sin(φ)  Equation (C).